Thermal Gravimetric Aspects

The copolymer with poly(phosphonic) acid in the ester form (structure 5) showed a first degradation step between 250 and 350°C. The magnitude of the step was directly correlated with the phosphonate ester content. This degradation was ascribed to the decomposition of the ester units to form ethylene and phosphonic acid units, possibly followed by a subsequent formation and loss of water, by self-condensation at these high temperatures. A second degradation step was noted between 350 and 400 C, most probably connected with the cleavage of the C-P bond. The copolymers in the acid form showed a small initial weight loss already from 150°C, ascribed to reversible self-condensation and desorption of 

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With respect to the intended applications, the thermal durability at inert conditions and, in particular, in air is the most crucial feature. Regrettably, often this aspect is discussed in the literature in a confusing manner. Mostly, the onset of mass loss at raising the temperature as determined by Thermo-gravimetric Analysis (TGA), which is a dynamic method, is taken as the limit of structural stability. Structural transformations, usually occurring at lower temperatures, as well as long term stability and the behavior of the material in atmospheres relevant for applications (e.g. air) are frequently neglected. 

By the summer of 1929 I had obtained positive spectroscopic and gravimetric results to prove the existence of the hydrides of gold and silver and to estimate their heats of dissociation (4). I asked Bonhoeffer whether I could work on some aspect of the ortho-para-hydrogen conversion. He suggested that I try to find out first the mechanism of the thermal para-hydrogen conversion and then that of the catalytic conversion. 

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